Micro-Electro-Mechanical Systems (MEMS) microbolometers are wavelength-independent detectors that sense incident electromagnetic radiation by the temperature increase caused by the radiation's absorption in sensing elements. The sensing element includes a temperature-sensing material whose resistivity is dependent on temperature. The temperature (or rather temperature change) of the element then can be read-out by measuring the resistance of sensing element using associated pixel readout integrated circuit. Detectors can be used as a single pixel to detect temperature or arrayed in a focal plane array to form an image.
Microbolometers are typically optimized to detect infrared wavelengths in the 2-14 μm region where traditional photonic sensors are insensitive (as in the case of silicon-based charge-coupled device (CCD) or complementary metal-oxide semiconductor (CMOS) image sensors) or expensive to fabricate (as in the case of quantum-well devices). They can be used in cameras that have applications in night vision, surveillance/security, medical imaging, and search and rescue. Alternatively, a single pixel or small pixel array can be used for non-contact temperature sensing in mobile phones and other devices.
Relative to visible light imaging, infrared (IR) imaging using MEMS microbolometers suffers serious shortcomings in image and video performance. In addition to the fact that current IR imaging greatly lags visible imaging in resolution, modern IR imagers exhibit insufficient dynamic range and insufficient grey-scale allocated to areas of interest such as human subjects or other warm objects. In scenes with motion, scrolling shutter artifacts occur such as wobble, skew, smear, partial exposure, and aliasing. Because of readout and sensor limitations, capture times are long and consequently, frame rates are low. Finally, de-noising, image enhancement, and image post-processing are inadequate. While performance of the microbolometer structure itself has made advancements with new designs, materials and fabrication methods, implementation of improved readout technology has yet to follow to match sensor gains.
Furthermore, although infrared imaging using microbolometers has found widespread applications in military, industrial and consumer products, their use has generally been limited to high-cost, low-volume products primarily because of the high cost of the microbolometer imager itself, which can account for about 50% of the total imaging system cost. Major contributors to the imager cost are the relatively large pixel size required to achieve acceptable device sensitivity and typically high yield loss due to pixel to pixel performance variation (among other contributors). State-of-the-art microbolometer pixel pitch is currently 17 um, or roughly 200 times the area of state-of-the-art visible-light CMOS image sensor pixels. Such relatively large pixel size results in a large array area, a large die size, and therefore fewer die-per-wafer, lower yields and high cost. Furthermore, a large array necessitates larger optics and optical paths which contribute to larger and more expensive systems. Therefore, improved yield and smaller pixel size can reduce imager and system costs in various ways enabling adoption of microbolometer infrared imaging into more price sensitive and higher volume products.